Method of producing a steel packing strip of high strength



3,551,216 METHOD OF PRODUCING A STEEL PACKING STRIP OF HIGH STRENGTHHerbert Severing, Hohenlimburg, Dieter Radtke, Letmathe, Hans-WilhelmGrasshofi, Hagen, and Heinz Kress, Holzen, Germany, assignors to HoeschAktiengesellschaft Hauptverwaltung, Dortmund, Germany No Drawing. FiledOct. 3, 1968, Ser. No. 764,955 Claims priority, application Germany,Nov. 23, 1967, 1,608,163 Int. Cl. C21d N26 US. Cl. 148-12 5 ClaimsABSTRACT OF THE DISCLOSURE A steel packing strip with a tensile strengthof around 95 to 125 kp./mm. an elongation 6 of 10 to 17% and a yieldpoint ratio of 0.86 to 0.98 is produced from a hot rolled steel strip ofa composition of about 0.35 to 0.80% C., 0.15 to 0.50% Si, possibly asmuch as 0.045% of P and S, 0.4% to 2% Mn and/r Ni, and the balancesubstantially all iron of sorbitic or intermediate stage structure afterhot rolling to the desired thickness of about 0.30 to 1.30 mm. is coldrolled and is finally subjected to a continuous brief recovery annealingwith the beginning of recrystallation at a temperature between about 500and 680 C., Mn and/or Ni content decreasing with increase in the contentof carbon.

BACKGROUND OF THE INVENTION (1) Field of the invention The inventionrelates to a process for producing a steel packing strip of highstrength with a tensile strength of about 95 to 125 kp./mm. anelongation 6 of to 17% and a yield point ratio of 0.86 to 0.98.

(2) The prior art It is known to produce packing strip with a tensilestrength of less than 96 kp./mm. by the relaxation and recoveryannealing of cold rolled strip of a steel of the type of DIM 1624, aswell as undeoxidized, half-deoxidized or completely deoxidizedstructural steel with additives corresponding to-DIN 17100 with thedesired tensile strength value. The relaxation and recovery annealingcan be carried out in continuous, pot or cupola annealing ovens. Thehigh strength packing strip with a tensile strength of more than 95kp./mm. is produced in a known way through a continuous or intermittentheating in two heat treatments from a steel with a composition of about0.20 to 0.40% C., 0.15 to 0.50%, Si, 1.0 to 1.5 Mn and, times, as muchas 0.35% P and S.

A disadvantage of packing strips with a tensile strength of less than 95kp./mm. is that they require a quite large cross section and for thesame reason also substantial weight, in order to have adequate packingcharacteristics. A further disadvantage in the production of packingstrips with a tensile strength of more than 95 kp./mm. is that two heattreatments are required, so that a yield point of only 0.75 to 0.85 isobtained.

SUMMARY OF THE DISCLOSURE The purpose of the present invention is toovercome these disadvantages in the known processes for the productionof packing strips and to produce a packing strip which has a tensilestrength of around 95 to 125 kp./ mmP, an elongation 6 of 10 to 17% anda yield point ratio of 0.86 to 0.98, which can be carried out in asimple manner with only one heat treatment.

"United States Patent 0 3,55 1 ,Z l 6 Patented Dec. 29, 1970 "ice Thisis achieved according to the invention by starting with a hot rolledstrip with a composition of about 0.35 to 0.80% C.

0.15 to 0.50% Si possibly 0.045% P and S 0.40 to 2.0% Mn and/or NiCbalance substantially all iron of sorbitic or intermediate stagestructure after the hot rolling to the desired thickness of around 0.30to 1.30 mm. is cold rolled and finally subjected to a continuous briefrecovery annealing with the beginning of recrystallization attemperatures of 500 to 68 C. In order to obtain the desired mechanicalcharacteristics, advantageously the carbon content of the steel stripused is varied inversely with that of the manganese and/or nickelcontent. Because the carbon content influences strongly the Working inhot and cold rolling, it is advantageous for the production of packingstrip according to the invention to use a steel strip With a carboncontent of 0.40% and manganese or nickel of 1.5 to 2%. If a steel stripwith a higher carbon content than 0.40% is used, then according to theinvention the manganese and/or nickel content is correspondinglyreduced. A further advantageous embodiment of the process according tothe invention is to wind up the steel strip after the hot rolling at areeling temperature of between 500 and 620 C.

The advantages achieved according to the process of the invention areespecially that, for the production of a high yield point ratio of about0.86 to 0.98 with a simultaneous elongation of 10 to 17% and a tensilestrength of 95 kp./mm. only one heat treatment for a very short time andat a reduced temperature is necessary, and, in contrast to a packingstrip with a tensile strength of less than 95 kp./mm. and an elongationof 6 to 10%, the new packing strip can be more highly loaded, so as tosave weight.

to the invention.

A steel strip with a composition of 0.47% C. 0.018% P 0.21% Si 0.014% S1.43% Mn balance iron is hot rolled to 1.50 mm. and is reeled at atemperature of about 560 to 580 C., so that for the subsequent coldrolling a sorbitic starting structure is obtained. Without difiiculty(such as production of cracks in the edges of the strip) this hot stripis cold rolled to 0.5 or 0.8 mm. and finally in an annealing oven issubjected in the presence of a neutral protective gas at a temperatureof 600 C. for two minutes to a recovery annealing (with a beginning ofrecrystallization). After this annealing treatment a finished packingstrip with a full mechanical characteristic is measured:

Yield Tensile point strength Yield 0' 1B Elongation ratio, kp./mm.kpJmm. 6 percent o'S/a'B Band thickness, mm:

gation 6 of 10 to 17%, and yield point ratio of 0.86 to 0.98, in which:

a hot rolled steel strip with a composition:

0.35 to 0.80% C 0.15 to 0.50% Si 0.40 to 2.0% of a metal selected fromthe group consisting of Mn and Ni balance essentially all iron with atensile strength of about 95 to 125 kp./mm. elonrolling to a thicknessof about 0.30 to 1.50 mm. is cold rolled and thereafter subjected to acontinuous brief recovery annealing with a beginning ofrecrystallization at temperature between 500 to 680 C., the content ofsaid metal being substantially inversely proportional to the carboncontent.

2. Process according to claim 1 in which said composition includes notmore than 0.045% P and S.

3. Process according to claim 1 wherein the steel strip after the hotrolling and before the cold rolling is reeled at a reel temperature ofabout 500 to 620 C.

4. Process according to claim 1 in which recovery annealing is carriedout in an oven.

5. Process according to claim 1 wherein the recovery annealing iscarried out in the presence of an inert protective gas.

References Cited UNITED STATES PATENTS 2,814,578 11/1957 White 148l23,264,144 8/1966 Frazier et a1. 14812 3,311,512 3/1967 Mohri et a1.14812.1 3,421,951 1/1969 Shelton 148--12.1

L. DEWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant ExaminerUS. Cl. X.R. 148-12.1

